If you use a script to mass edit your Reddit content, make sure you make it wait a few seconds between each edit. If you do the mass editing by hand, make sure you're not too fast.

Otherwise, it will appear like the edit was successful, but if you reload the page, you'll see it didn't actually take.

I've found a link to this fork of Power Delete Suite in the comments somewhere here in the fediverse and it worked because it waits for 5 seconds between edits. Warning: If you want a backup of your comments before editing them though, use the main Power Delete Suite to get it that, the fork's version of the backup was incomplete (I ran the backup first, looked for my very first Reddit post and it wasn't there, so I was glad I hadn't run the editing portion yet. When I ran the main version of PDS I got a complete backup. It's only the backup that's incomplete in the fork though, the editing caught everything once it had slogged through.)

PS 1: Reddit seems to be undeleting deleted stuff sometimes, but they don't seem to keep edit history.

PS 2: Some subreddits seem to remove all comments edited after/before some point in time or passed time period, some seem to remove all comments edited to mention lemmy/kbin.

PS 3: It is not possible to delete or edit or even see your own content in subreddits that are currently set to private. As subreddits go from private back to public, you'll need to go back and edit that newly visible and editable stuff.

Edited to add: You should know this because most likely you have a reddit account and you might wish to purge it and replace the content you gave them with an explanation of why you left reddit or a "fuck /u/spez" or an invitation to the fediverse.